Remove some unnecessary uses of `struct_span_fatal`
Remove some unnecessary uses of `struct_span_fatal`

All of them immediately called `emit()` then `raise()`, so they could
just call `span_fatal` directly.

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust